This invention relates generally to the manufacture of semiconductor integrated circuits and, particularly, to photolithography processes for manufacturing such circuits.
In the manufacture of semiconductor integrated circuits, a photoresist film is formed over a semiconductor wafer. The photoresist film may be irradiated so that some regions of the photoresist film are either harder or easier to dissolve in aquesios base developer. As a result, a pattern can be repeatedly transferred to the semiconductor wafer via the photoresist film. After developing, the photoresist film may be used as a mask for etching desired features in the underlying layers of the semiconductor wafer.
Advances in photolithography techniques utilized to transfer patterns to photoresist have enabled increasingly smaller patterns to be transferred. This means that smaller integrated circuit features can be formed in integrated circuits. As a result, more elements can be put in a given area on a semiconductor integrated circuit. One result of these advances has been to reduce the cost of integrated circuits.
One advanced photolithography technology is extreme ultraviolet technology (EUV). For current chemically amplified photoresists, the photoacid generators (PAGs)are the components in the resist formulation. These photoacid generators generate acids upon exposure to appropriate irradiation. The generated acids will cleave the protecting groups on the resins and switch the photoresist's solubility in the base aqueous developer.
Photoacid generators developed for prior photo-lithography technologies may achieve relatively good quantum yields at the required wavelengths. However, these photoacid generators will outgas under extreme ultraviolet irradiation under vacuum. Outgassing is the release of gases or vapors by a material over time. Outgassing may result in degradation of the lens used in the extreme ultraviolet optics due to photoresist fragment deposition related to outgassing.
Currently, photoacid generator technology has focused primarily on perfluoroalkyl sulfonate (PFAS) anion and phenyl-based cation photoacid generators. However, the cation portion of the photoacid generators of this type will outgas after extreme ultraviolet irradiation.
Traditionally, photoactive compounds, such as diazonapthoquinone (DNQ), with Novalac have been used I-line (and G-line) as a two component photoresist. However, the contrast achievable with such a structure limits the resolution of that photoresist.
As the acid diffusion length decreases, chemical amplification may be less efficient. The typical spacing between de-protecting groups is typically a few nanometers apart. When the acid diffusion length that is required to meet resolution targets becomes equivalent to the spacing between protecting groups, the photoacid generator no longer acts a chemical amplifier because the photoacid generator interacts with only one de-protecting group on average.
Since chemically amplified resists reach a point where they are no longer efficient, alternatives to chemical amplification are needed. Thus, there is a need for ways to enable even smaller feature sizes to be transferred by photolithographic processes.